Tyrosine is a nonessential amino acid the body makes from another amino acid called phenylalanine. It is a building block for several important neurotransmitters, including epinephrine, norepinephrine, and dopamine. Neurotransmitters help nerve cells communicate and influence mood. Tyrosine also helps produce melanin (the pigment responsible for hair and skin color) and helps in the function of organs responsible for making and regulating hormones, including the adrenal, thyroid, and pituitary glands. It is involved in the structure of almost every protein in the body.
Tyrosine deficiencies are rare. Low levels have been associated with low blood pressure, low body temperature, and an underactive thyroid. This does not mean, however, that taking tyrosine supplements will improve any of these conditions.
This serious condition occurs in people who cannot metabolize the amino acid phenylalanine and leads to brain damage, including mental retardation. People with PKU must avoid any phenylalanine in their diets. Because tyrosine is made from phenylalanine, people with PKU can be deficient in tyrosine. Tyrosine is used in protein supplements for people with PKU, but most doctors don't recommend more tyrosine supplements. If you have PKU, your doctor will determine if you need more tyrosine and how much.